When functioning properly, the human heart maintains its own intrinsic rhythm and is capable of pumping adequate blood throughout the body's circulatory system. However, some individuals have irregular cardiac rhythms, referred to as cardiac arrhythmias, which can result in diminished blood circulation and cardiac output. One manner of treating cardiac arrhythmias includes the use of a pulse generator, such as a pacemaker, an implantable cardioverter defibrillator (ICD), or a cardiac resynchronization (CRT) device. Such devices are typically coupled to a number of conductive leads having one or more electrodes that can be used to deliver pacing therapy and/or electrical shocks to the heart. In atrioventricular (AV) pacing, for example, the leads are usually positioned in a ventricle and atrium of the heart, and are attached via lead terminal pins to a pacemaker or defibrillator which is implanted pectorally or in the abdomen.
Magnetic resonance imaging (MRI) is a non-invasive imaging procedure that utilizes nuclear magnetic resonance techniques to render images within a patient's body. Typically, MRI systems employ the use of a magnetic coil having a magnetic field strength of between about 0.2 to 3 Teslas. During the procedure, the body tissue is briefly exposed to RF pulses of electromagnetic energy in a plane perpendicular to the magnetic field. The resultant electromagnetic energy from these pulses can be used to image the body tissue by measuring the relaxation properties of the excited atomic nuclei in the tissue. In some cases, imaging a patient's chest area may be clinically advantageous. In a chest MRI procedure, implanted pulse generators and leads may also be exposed to the applied electromagnetic fields.